Electron tube



R. scHwElZER ELEc'rRoN TUBEl May I, 1951 Filed May 29, 1945 Patented May I; 1951 Rudolf Schweizer, Zurich;V ESwiterland, assignor to Aktiengesellscliaft Brown, Boveri & VCie.,

Baden, Switzerland Application May 2'9, 1945, Serial No. 596,479

In Switzerland June 20, 1944 6 Claims. Cl. 250-275) i 1 With -the electron ltubes which have 'so far Vbeen developed for the decimetre wave range no iappreciable and stable amplification can be obtained if the material and size required is to be kept within 'reasonable limits. 'all due to the 'fact that the usual tubes for these wave lengths have input resistances which are j too small. VIt has already been proposed with pentodes to increase the input lresistances by compensation in the screen grid. This measure* Vis, however, only effective with wave lengths above 1.5 metres.

Conditions are just as unfavourable with mixer tubes. Nowadays for decimetre Waves practically exclusively diodes are used; these, however, have a strong attenuation effect on the input and output circuts and furthermore represent an undesirable coupling between the circuts which are to be mixed.

Objects of the present invention are to provide electron tubes which overcome the drawbacks and defects of the tubes previously employed in the decimeter wave range. Objects are to provide electron tubes in which two anodes are located'in the same electron or space current path and are connected in parallel to the same source of anode current; and at least one control grid is so positioned with respect to the anodes and Va common cathode that the grid voltage-anode current characteristics of the two anodes are -of 'opposite slope, i. e. a change in grid potential increases the electron current to one anode and `decreases'the'electron current to the other anode.

Objects are toprovide electron tubes 'having a pair of anodes and a control grid system which alters the distribution of the electron current to the anodes, but not the total electron current, upon a change in control grid potentiah -Objects are to provide tubes having the characteristics stated, and in which the control grid or control grids may he biased negatively to draw no current.

These and' otherobjects :and the advantages of the invention will be apparent from the following specification when taken with the, accompanying drawings in which;

Fig. 1a is an elevation of an electron tube embody-ing the invention; f i 1 jF-fig. 1b vis a transverse section as taken on line :zi-x of Fig. 1a;

Fig. 2 is a schematic view of another embodiment of-theinvention; f w

I 1Fig. l3 is va 'cu-rve sheet showing typical` grid voltage-anode current characteristics for there- This is above when the grid potential varies.

. o 2 o spective anodes of tubes embodying the invention; 1 t

Fig. 4 is a transverse section through another 'e'mbodiment of the invention;

Fig. 5 is va schematicdiagram of a circuit including a tube constructed as 'shown in Fig. 4; and z Fig. 6 is a circuit diagram of a direct current amplifier employing tubes of' the Fig. 4 construction. y

InV Figs. 1a and 1b, the reference character K identifies an annular cathode which is fixed to the rod-shaped defiector 'electrode AE. G is a hollow cylindrical grid and A1, Az are two hollow cylindrical anodes arranged coaxially with the grid G and the cathode K. The deflector electrode AE which is at cathode potential causes a 'sufficiently large part of the primary electrons to reach the anode A1. The anodesare spaced axially from the cathode K 'by different distances; the larger diameter anode A1 being closer to the cathode K than the smaller diameter anode Az, and the relative axial displace- 'inents are such that the electron paths from the cathode to the respective anodes are of substantially equal mean length. The cylindrical grid G extends through the anode A1 and its 'that the voltage drops R111 i1 and' Raz iz occurring across' the resistances 'Ren and Raz respectively vary to the same extent but in the opposite sense If necessary they can be corrected in this respect by correspondingly dimensioning the resistances Rai, Raz. 'By this means no voltage fluctuations with resulting reactions on the primary electron circuit occur in the common part of the external anode circuit. i

In order to suppress the disturbing influence of the grid-anode capacitance, anodes A1, Az and grid G are constructed and arranged in such` a man'ner that the -capacitances Cga1 and Cgciz (Fg; 2) equal-'each other and jare as small 'as possible. `V4With the constructional example shown in Fig. l'this 'is achieved by the grd G on the one handpenetrating the anode A1 and on the other hand enclosing the anode Az. Particularly favourable grid-anode capacity conditions are obtained by means of a symmetrical assembly 'of the electrodes. Such an electron tube is shown in Fig. 4 in cross-section. With this construction two grids G1, Gz are used and each anode A1, A2 consists of a part arranged outside the associated grid and a part located between the other grid and the cathode K, this latter part being constructed with perforations.

The input resistance Re of the tube consists mainly of the resistance of the grid-anode capacitances Cgai, Cgaz and the working resistances Rai and Raz which with reference to the grid G are connected in parallel. When it is assumed that R Ra,=Ra2=-2 the tube has an input resistance;

where i is 1.' Thus even in the most unfavourable case, that is with very short Waves, where the capacitive resistance becomes very small, there will be an input resistance Ra Re 'i When the tube vis used for transmitting purposes the capacitance between the anode with negative characteristic and its associated grid is preferably selected greater than the capacitance between the other anode and its associated grid, so that no special feed-back circuit is required. The smaller the transconductance of the tube the greater must be the difference between the individual grid-anode capacitances.

By this means furthermore the upper limiting frequency of the tube depends solely on the velocity of the primary electrons.

Fig. 5 for instance shows an arrangement of an oscillator with a symmetrically constructed electron tube according to Fig. 4, S being the tank circuit of the oscillator. The high frequency oscillations are completely confined to the part of the tube containing the grids G1. G2 and anodes A1, Az, so that the travel time of the electrons between this part of the electrode system and the cathode is of secondary importance. It is therefore possible to accelerate the electrons emitted from the cathode by known means such as a positive potential impressed upon a special grid G3 and thus raise the upper limiting frequency of the tube very considerably.

By means of a control grid G4 located between cathode K and grid G8 it is also possible to modulate the high frequency generated in the oscillator practically without power (pure amplitude modulation). The tube can also possess a grid G5 for stopping the secondary electrons coming from the anodes A1, A2.

Electron tubes with an arrangement of electrodes such as are shown in Figs. 4 and 5 can also be used as mixer tubes. In this case the high frequency oscillation is applied to grids G1, G2 and the auxiliary oscillation to the control grid G4, the intermediate frequency alternating voltage being taken from circuit S which is QQL- nected between the anodes A1, Az.

Number Fig. 6 shows how electron tubes according to Fig. 4 can be used for direct current amplification.` The low frequency direct or alternating voltage is supliedto the amplifier over terminals e, the amplified voltage being obtained at terminals 7). The amplifier tubes are indicated by E1, E2 and Z is a measuring instrument.

The current control according to the invention can also be used in tubes with more than two anodes, for intance in a rotating field arrangement.

I claim:

1. An electron tube comprising a cathode, a pair of anodes having cylindrical surfaces coaxial with said cathode and spaced therefrom by electron paths of substantially equal mean lengths, said anodes being adapted to be connected in parallel to the same source of energizing potential through an external anode circuit having a part in common, and means located between said cathode and the respective anodes to control simultaneously and in opposite sense the instantaneous distribution of the electron current to the separate anodes, said control means comprising grid means upon which alternating control voltages may be impressed; whereby said anodes have grid voltage-anodeicurrent characteristics of opposite slope and control voltages impressed upon said grid means do not develop voltage fluotuations in said common part of the external anode circuit.

2. An electron tube as recited in c'laim 1, wherein said anodes are coaxial cylindrical elements, and said grid means is a cylindrical e1ectrode surrounding one anode element and within the other anode element.

3. An electron tube as recited in claim I, wherein said grid means includes individual grids located in the electron path between said cathode and the respective anodes.

4. An electron tube as recited in claim 1, wherein said grid means includes individual con' trol grids located in the electron path between said cathode and the respective anodes, and each anode includes a section positioned out- Wardly of the associated control grid and a perforated section located between the other control 'grid and said cathode. p

5. An electron tube comprising a cylindrical cathode, a pair of anodes symmetrically located at opposite sides of said cathode, and control grids located between the cathode and each anode, each anode including a perforated section located between the cathode and the control grid associated with the other anode.

6. An electron tube as recited in claim 5, in combination with a cylindrical grid surrounding said cylindrical cathode and located between the same and said control grids.

i RUDOLF SCHWEIZER.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Name Date 1,850,104 Hansell Mar. 22, 1932 2,156,088 Heising Apr. 25, 1939 2200330 Engbert May 14, 1940 2,235,498 Herold Mar. 18, 1941 2.245,159 Samuel June 10, 1941 aame gray Oct. 7, V19741 

